There is conventionally known, as an underwater welding apparatus that performs underwater welding, an underwater welding apparatus that performs underwater repair for an in-reactor structure provided in reactor water of a nuclear reactor. Such an underwater welding apparatus needs to be configured to form underwater, at least around a welding pool, a space where water is excluded by means of gas during welding. Thus, various methods have been proposed to ensure a partial shield for forming the space where water is excluded around the welding pool.
For example, in an underwater machining apparatus described in Patent Document 1, when a material 1 to be processed as a material to be welded provided in an underwater environment is welded as illustrated in FIG. 7, a TIG welding power supply 2 is installed in the atmosphere, and only a welding torch 4 which is a welding head from which an arc 3 is generated is installed underwater. In this state, shield gas 6 is used to locally exclude water (welding part is shielded) so as to prevent the welding torch 4 and welding part 5 from contacting the water.
Moreover, the underwater machining apparatus described in Patent Document 1 uses, as a shield means for excluding the water, a combination of a highly elastic shield cover (solid wall) 7 made of a felt-like cloth woven from carbon fibers each having a thickness of about 5 mm and Ar gas.